In particular, when you play piano, one of the key elements is making dynamics with your touch. If you want the piano to sound louder, you play with more force. If you want to play softer, you use less force. It’s as simple as that.
But on the organ, the dynamics are not achieved through the same techniques that pianists use. On the organ, in order to increase or decrease the volume, you can change the registration or manipulate the swell box.
Sure, you can make subtle accents with some clever use of articulation and touch (on the mechanical action organs) but what I want to stress here, is that you should not use that excess force.
There is simply no need to pound on the keys harder if you are playing a loud piece. On the contrary, the softer you depress the keys, the better you will be able to control the releases which are equally or more important than the depression of the keys.
So you have to be relaxed enough and play mezzo piano on the organ. Use only as much power as is needed to depress the keys.
By the way, do you want to learn my special powerful techniques which help me to master any piece of organ music up to 10 times faster? If so, download my video Organ Practice Guide.